Millisecond pulsar with the highest rotation speed discovered in the galactic field

Some LOFAR antennas and the positions of PSR J1552+5437 and PSR J0952-0607 (Image NASA/DOE/Fermi LAT Collaboration and ASTRON)

An article published in “The Astrophysical Journal” describes the discovery of PSR J0952-0607, the millisecond pulsar with the highest rotation speed in the galactic field. A team of researchers used the Low-Frequency Array (LOFAR) radio telescope to investigate high-energy sources detecting this pulsar that spins at over 42,000 rotations per minute, 707 per second.

A pulsar is a neutron star, one of the possible remnants of a star that exploded in a supernova. A mass that may be higher than Sun’s is compressed into a sphere that has a diameter of a few kilometers. Its magnetic field powers electromagnetic radiation rays at various frequencies that can be seen as regular pulses, hence the name pulsar for this type of object.

Millisecond pulsars have a rotational period between 1 and 10 milliseconds. The origin of a pulsar with such a rapid rotation hasn’t been established but the most likely theory states that those are neutron stars that captured new materials from a companion star. The angular momentum transferred in this accretion would increase the pulsar’s rotation speed up to hundreds rotations per second.

The fastest known millisecond pulsar so far discovered, called PSR J1748-2446ad, almost reaches 43,000 rotations per minute. It’s inside the Terzan 5 globular cluster while the newly discovered one, PSR J0952-0607, is in a galactic field, outside a globular cluster. For this reason, it’s the pulsar with the fastest rotation among those on the galactic field and the second overall in the Milky Way.

The pulsar PSR J0952-0607 has a distance from the Earth currently just roughly estimated between 3,200 and 5,700 light years. Its mass was estimated to be around 1,4 solar masses and a companion orbits it that used to be a star but has now been reduced to a gas giant with a mass almost 20 times Jupiter’s. These systems have been nicknamed “black widows” because the neutron star steals materials from a companion and eventually ends up devouring it completely.

The discovery of the pulsar PSR J0952-0607 occurred following the detection of various gamma ray sources. NASA’s Fermi Space Telescope allowed to map several sources of this type and about a third of them haven’t been detected at other wavelengths. Many of them are pulsars but further investigations are needed to verify it and often that’s done with observations at the other end of the electromagnetic spectrum, meaning at radio waves.

The LOFAR radio telescope is an international network of antennas designed to observe the universe at frequencies between 10 and 250 MHz. It detected pulses from the pulsar PSR J0952-0607 at about 135 MHz, a much lower frequency than those generally monitored in radio searches.

A similar situation was found with the first millisecond pulsar discovered with LOFAR, called PSR J1552+5437, which rotates at about 25,000 rotations per minute. LOFAR’s sensitivity at emissions of that type of pulsars makes researchers hope to find more ultra fast ones to better understand those extreme objects.